Unfairness is the noun for a situation where people are not treated equally or reasonably — where someone gets less than they deserve, or others get an advantage they did not earn. It is the name for the thing itself, not for the feeling about it: 'the unfairness of the system'. English uses it in two slightly different shapes, and mixing them up is the usual student error. Uncountable, with no article or with 'the': 'unfairness in the workplace', 'the unfairness of it all'. This is the normal use — unfairness as a quality spread through a situation. Countable, in the plural: 'the small unfairnesses of daily life' — separate individual unfair things. That plural is rarer and a bit literary. You will meet it most in serious writing about work, school, law, money, and society: 'a deep sense of unfairness', 'to complain about the unfairness of the rules', 'perceived unfairness' (people feel it is unfair, whether or not it is). Notice 'a sense of unfairness' — that fixed phrase is how English usually talks about the experience of being treated badly, and it is very common in news and social writing. In ordinary speech, though, people rarely reach for the noun. They say 'that's not fair' or 'it's so unfair'. The noun belongs to writing, to arguments, to essays — which, for a student taking exams, is exactly where you need it.